having gas smell issues

i have a smell of gas coming while driving car ..the gas cap has alot of pressure an the code of 0441 cAME UP ON TESTER ..WHILE I WAS CHECKING GAS CAP ?? I SEE A CANISTER AN VALVE IN THE AREA OF THE INLET ..I HEAR A NOISE THERE AN IT SMELL OF GAS ..HOW DO I CHECK THIS TO SEE IF THIS IS THE ISSUE??
I SMELL GAS BACK THERE TOO ..THERE IS NO LEAKS I CAN SEE OR FOUND AT ALL .
CAR SEEMS TO USE ALOT OF GAS ALSO ..
ITS A 5.7 LITER
AUTO MATIC
THANKS FOR YOUR HELP